(1) Field of the Invention
The present invention relates to determination of the contour of a surface from a position located remotely of the surface and particularly to measuring the profile of the surface of charge material which has been deposited on the hearth of a furnace. More specifically, this invention is directed to apparatus for use in determining the profile of the surface of the burden in a shaft furnace and particularly a blast furnace employing a bell-less charging installation. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
It is well known that proper exercise of control over the profile of the burden of a blast furnace is essential to maximizing the efficiency of operation of the furnace; i.e., the exercise of control over the charge profile is necessary in the interest of insuring that the furnace throat gases will pass through the charge in the optimum manner. Thus, by way of example, if the level of the burden is too low at the center of the furnace in comparison with its level at the periphery, for example as a result of excessively rapid subsidence at the center, the distribution of the various materials with which the furnace is being charged can not be accurately controlled since certain materials will tend to become concentrated in the centers and others at the periphery in accordance with their granulometric configuration and the angle of the slope formed by the materials. The resulting "V" shaped charge profile tends to become accentuated since the greater of the depth of the "V" at the center of the furnace the more the furnace will "draw" in that position with consequently more rapid descent of the central part of the burden. If, on the other hand, the "V" shape of the charge profile is very slight, or if the level of the charge is higher at the center than at the periphery of the furnace, there is a risk that the furnace will "draw" mainly at its periphery. This phenomenon is known in the art as "peripheral movement" and causes an excessive temperature rise in the refractory walls of the furnace.
It is also known that the surface contour assumed by charge material deposited on the hearth of a blast furnace; i.e., the profile of the furnace burden; is essentially determined by two factors. The first of these factors is the manner in which the material is distributed when introduced into the furnace. The second profile determinative factor is the nature of the uneven descent of the material as it falls under the influence of gravity to the hearth after having been introduced into the furnace.
Two basic types of shaft furnace charging devices are presently known in the art. The first, which has been in use for many years, employs two superimposed charging bells. In charging installations employing such charging bells, the profile of the charge surface is determined solely by the descent of the charge material inside the furnace and it is well known that a depression or hollow is unavoidably formed at the center of the furnace; i.e., the charge profile has a characteristic M-shaped curve. The second category of charging device is a bell-less system which employs a rotatable and angularly adjustable charge distribution spout. Such a bell-less charging installation is shown and described in U.S. Pat. No. 3,693,812. Use of a bell-less charging installation with a steerable spout makes it possible to distribute the charge material in any desired manner on the furnace hearth and also to compensate for any changes which may occur as a result of a localized or uneven subsidence of the burden on the furnace hearth. Thus, a bell-less charging installation such as that described in U.S. Pat. No. 3,693,812 enables the exercise of a high degree of control over the way in which the surface profile of the burden on the furnace hearth develops. This desirable degree of control, however, may be exercised only if the existing charge profile can be determined.
As should be obvious from the above brief discussion, the development of devices which enable the profile or surface contour of the burden on the hearth of a furnace to be measured has attracted considerable attention. Efforts aimed at the development of such "profilometers" have been particularly intense since bell-less charging installations, wherein the charge material may be distributed as desired on the furnace hearth, have become available. However, prior to the present invention, there have been no reliable devices available which enabled the profile of the burden in the shaft furnace to be accurately determined.
The prior art charge profile measuring technique most frequently employed utilized one or more vertically movable probes. These probes were conventionally of the mechanical type, although radiation type probes have been proposed, and were distributed around the periphery of the furnace. These prior mechanical probes consist of rods or chains which are lowered vertically until the surface of the burden is contacted in order to determine the level of the burden in the vicinity of the furnace periphery. While these vertically movable mechanical probes offer the dual advantages of accurate measurement and lack of complexity, they suffer from the serious drawback of being able to indicate the height of the furnace burden only at a few peripheral points. Thus, prior art techniques provided very little information on the profile of the burden as a whole, particularly in the central zone.
It is to be observed that the advent of bell-less charging installations has made it possible to widen the annular zone, extending inwardly from the furnace wall, which may be sensed employing peripheral vertical probes. This enlargement of the area of the charge surface which may be probed results from the fact that the location of the probes is no longer impeded by the lower bell and impact ring of the prior bell-type charging devices. Nevertheless, even with the widened annular zone which can be sensed employing peripheral probes in modern blast furnaces, information concerning the charge height at the center of the furnace is still necessary in order to provide adequate information on the charge profile.
In view of the previous inability to sense the level of the burden on a furnace hearth at the center of the furnace through the use of a reliable mechanical probe, and particularly a movable probe, there have been attempts to perfect profile measuring instruments which emit beams or pulses of light or electromagnetic, ultrasonic or nuclear radiation. Such instruments, if they could be developed, would have the capability of being able to obtain a total representation of the profile over the entire surface of the burden. These radiation based profilometers, while offering a theoretical solution to the problem of measuring the charge profile within a shaft furnace, have to date been unsuccessful. The lack of success may be attributed to the exceedingly difficult operating conditions which include high temperature and pressure and the presence of a significant amount of dust.